# 速度换算器

> 使用精确系数将 mph 换算为 km/h、km/h 换算为 mph，以及 m/s 和节；还支持 ft/s、海平面马赫数和光速。

交互版本：https://www.calcopenly.com/zh/conversion/speed-converter
主题：单位换算器

Each speed unit is a fixed number of metres per second. The road and sea units are exact: a mile per hour is 0.44704 m/s because the mile is 1,609.344 m, a kilometre per hour is 1/3.6 m/s, and a knot, one nautical mile per hour, is 1,852/3,600 m/s.

The default converts 60 mph to 96.56064 km/h, the figure a UK or US driver needs on metric roads. Sailors and pilots work in knots, and 1 knot is exactly 1.852 km/h.

Mach is fixed here at 340.294 m/s, the speed of sound in the International Standard Atmosphere at sea level and 15 °C, and results that use it are marked approximate because the real speed of sound falls with temperature. The speed of light is exactly 299,792,458 m/s by definition.

## 输入

- **数值**: 输入源单位下的数值，也可以输入带有自身单位的数值
- **从** (选项：metre per second (m/s), kilometre per hour (km/h), mile per hour (mph), knot (kn), foot per second (ft/s), kilometre per second (km/s), Mach (sea level) (Ma), speed of light (c))
- **到** (选项：metre per second (m/s), kilometre per hour (km/h), mile per hour (mph), knot (kn), foot per second (ft/s), kilometre per second (km/s), Mach (sea level) (Ma), speed of light (c))

## 结果

- 转换后的数值 — 主要结果
- 换算
- 换算系数
- 精确性

## 公式

$$
\begin{gathered} x_{\text{to}} = x_{\text{from}} \times \dfrac{f_{\text{from}}}{f_{\text{to}}} \\ f = \text{one unit expressed in } \text{m/s} \end{gathered}
$$

## 计算示例

### 60 mph in km/h

- 数值: 60 mph
- 从: mile per hour (mph)
- 到: kilometre per hour (km/h)
- **转换后的数值: 96.56064 km/h**
- **精确性: 精确**
- 核验来源：60 × 1609.344 m / 1000 = 96.56064 km/h (1 mi = 1609.344 m, NIST HB 44)

### 1 knot in km/h

- 数值: 1 kn
- 从: knot (kn)
- 到: kilometre per hour (km/h)
- **转换后的数值: 1.852 km/h**
- 核验来源：1 knot = 1 nautical mile per hour = 1852 m/h (NIST SP 811 App. B)

### 100 km/h in m/s

- 数值: 100 km/h
- 从: kilometre per hour (km/h)
- 到: metre per second (m/s)
- **转换后的数值: 27.7777777778 m/s**
- **精确性: 定义精确，结果为循环小数**
- 核验来源：100000 m / 3600 s = 250/9 (Python 3.8 fractions from the legal definitions)

### Speed of light in km/s

- 数值: 1 c
- 从: speed of light (c)
- 到: kilometre per second (km/s)
- **转换后的数值: 299,792.458 km/s**
- 核验来源：c = 299,792,458 m/s exactly (SI definition of the metre)

### Mach 1 at sea level (approximate)

- 数值: 1 Ma
- 从: Mach (sea level) (Ma)
- 到: kilometre per hour (km/h)
- **转换后的数值: 1,225.0584 km/h**
- **精确性: 近似**
- 核验来源：340.294 m/s (ISA sea level, 15 °C) × 3.6 = 1225.0584 km/h

## 常见问题

### How do I convert mph to km/h?

Multiply by 1.609344: 60 mph × 1.609344 = 96.56064 km/h, and 70 mph is 112.65 km/h. The factor is exact because a mile is exactly 1,609.344 m. Multiplying by 1.6 is a mental shortcut that comes out 0.6% low; to go from km/h to mph, multiply by 0.621371.

### How do I convert km/h to m/s?

Divide by 3.6, because an hour has 3,600 seconds and a kilometre 1,000 metres. 100 km/h is 27.78 m/s and 36 km/h is exactly 10 m/s. Multiply by 3.6 to go back: a sprinter at 10 m/s is running 36 km/h, or 22.37 mph.

### What is a knot in mph and km/h?

One knot is exactly 1.852 km/h, about 1.15078 mph or 0.514444 m/s. It is one nautical mile (1,852 m) per hour, the speed unit of shipping and aviation, so a 30-knot wind is 55.56 km/h or 34.52 mph.

### How fast is Mach 1?

In the International Standard Atmosphere at sea level (15 °C) it is 340.294 m/s, which is 1,225.06 km/h or 761.22 mph, the value this converter uses. The speed of sound depends on air temperature, so at 11 km altitude, where the standard atmosphere is −56.5 °C, Mach 1 is about 295 m/s or 1,062 km/h.

### Why is the speed of light an exact number?

Because the metre is defined from it. Since 1983 the metre has been the distance light travels in vacuum in 1/299,792,458 of a second, which fixes c at exactly 299,792,458 m/s, or 1,079,252,848.8 km/h. Converting c into any unit here is therefore exact.

### “速度换算器”有多准确？

准确性取决于输入值和方法的假设。十进制运算使用50位有效数字，但估算、数值方法和源数据的精度可能较低；显示时的舍入并不能消除这些限制。 已按独立来源核验的计算示例：5。 例如，“60 mph in km/h”根据60 × 1609.344 m / 1000 = 96.56064 km/h (1 mi = 1609.344 m, NIST HB 44)进行核验。

### 这种方法出自哪里？

NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors; NIST Handbook 44, Appendix C — General tables of units of measurement.

## 来源

- [NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44, Appendix C — General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)